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The federal government will require each agency to measure its greenhouse-gas emissions for the first time and set targets to reduce them by 2020, under an executive order signed by President Obama Monday.

The measure affects such things as the electricity federal buildings consume and the carbon output of federal workers' commutes.

"As the largest consumer of energy in the U.S. economy, the federal government can and should lead by example when it comes to creating innovative ways to reduce greenhouse gas emissions, increase energy efficiency, conserve water, reduce waste, and use environmentally-responsible products and technologies," Obama said in a statement. "This executive order builds on the momentum of the Recovery Act to help create a clean energy economy and demonstrates the Federal government's commitment, over and above what is already being done, to reducing emissions and saving money."

Each agency must report its 2020 emission targets to the Council on Environmental Quality within 90 days.

Administration officials said they could not estimate the federal government's carbon footprint, since it has never been measured before, but the government ranks as the nation's largest energy consumer. It occupies nearly 500,000 buildings, operates more than 600,000 vehicles and employs more than 1.8 million civilian workers.

Under the executive order, all federal agencies will have to meet a series of environmental targets over the next decade. They include 50 percent recycling and waste diversion by 2015; a 30 percent reduction in vehicle-fleet petroleum use by 2020; and a 26 percent improvement in water efficiency by 2020.

President George W. Bush signed an executive order in 2007 that asked four agencies to draw up regulations to reduce greenhouse-gas emissions from cars and trucks by the end of his administration, but didn't ask for specific targets. His move came after the Supreme Court ruled that his administration did not follow Clean Air Act requirements in not regulating greenhouse-gas emissions from motor vehicles.

Rep. Earl Blumenauer (D-Ore.), who chairs the new House Democratic Livability Task Force and has pushed for more money for low-carbon transportation, said the new policy made sense fiscally as well as environmentally.

"Taxpayers shouldn't be paying for Washington's inefficiencies, and I'm speaking of the incredible energy and fuel wasted in our government buildings and vehicle fleets," Blumenauer said. "As the biggest landlord in the nation, we need to show leadership by reducing fuel use, cutting costs, and improving the operations of our agencies' fleets and buildings."